Sure. Here's my process:
First, I split up the adventure into fourths, with about 15-20 entries per part. Then I roughly set the difficulties for each part like so:
* First part is mostly d6's with some d8's.
* Second part is mostly d8's with some d6's and some d10's.
* Third part is mostly d8's and d10's with a few d12's.
* Last part is mostly d10's and d12's.
I sprinkle in a few outliers here and there, but that's the basic structure.
Then I put in the twists and plot points. You always want at least six challenges between each plot point so there's always at least one challenge between them.
More plot points and complicated twists (like the vikings in the Frost Giant adventure) take up space, so the more of these you have, the fewer entries total you'll have if you want them to fit on the 'zine, which in turn means that you might need to ramp up the d10's and d12's to add a little difficulty since the player will do fewer challenges. (Unless those twists make things harder, in which case, you might need to ramp things down.)
I lay it all out in a word processor. If you want it to match the style of the existing adventures, you'll want your "pages" to be 2.75"x4.25" with 0.2" margins, laid out 8 to a page on an 8.5"x11" page. The font is "Charter", and here are the various font sizes:
* Body is 9pt roman.
* Plot points are 8pt italic.
* Headers are 15pt bold with underscores.
* Title is 22pt bold.
The image is 2.35"x2" with a 2pt black border. I draw it by hand with a ballpoint pen and scan it in. The lock, fight, and treasure images are just Emoji.
I'll tweak the plot points and challenges a bit so they flow nicely on the pages and don't crete orphans.
Then I playtest! I don't release an adventure until I've beaten it, and if it seems too easy or too hard, I'll go in and tweak some of the challenge difficulties.
If you make some "Dungeon Hero" zines, let me know, and I'll share them with my followers on Twitter!